I can't count the number of novels, plays, and movies ruined for me because I'm so picky about plausibility. "Wait, why would he do that?" I ask myself so loudly, it drowns out the story's own dialog. "Why didn't the CIA notice that?" "Where did she get that rope?"
Rarely would I raise this complaint about 007 movies, say, which routinely defy the laws of physics (let alone the probability that a trained marksman will hit his target) in the name of escapist entertainment. That said, the eternal question of "where does the Highlander stash his sword when he rides his motorcycle?" is, over time, wearying.
The problem mainly bothers me in more serious, introspective, or supposedly frightening works, where a deus (or simply a res) ex machina and downright magical luck can sever my connection to the narrative and my belief in the characters. Being picky is a curse, but many curses can be re-conceived as blessings. My duty, then, is to use my overactive incongruity sensor to improve the details of the plots I write.